Light Emission

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Light Emission
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Todays Topics

• Excitation
• Emission Spectra
• Incandescence
• Absorption Spectra

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Excitation/De-Excitation

• Electron raised to higher energy level
• Electron emits photon when it drops back down to
  lower energy level
• Ef
• E hf (h is Plancks constant more later)
• h 6.626 x 10-34Js

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Incandescence

• Glowing while at a high temperature
• Caused by
• Electrons emit
• Peak frequency depends on
• Intensity of radiation depends on

Frequency is proportional to the absolute
temperature
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Emission Spectra

• Continuous Spectra
• Bright Line Spectra

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Absorption Spectra
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Fraunhofer Lines

• Spectrum produced by sun is not continuous
• Similar lines in spectra produced by
• Lines indicate the sun and stars are

Joseph Fraunhofer (1787-1826)
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Hydrogen
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Fluorescence

• Photon
• Electron
• Electron

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Fluorescent Lamp
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LASER

• L A through S
  E of R

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Lasing Medium is Pumped

• Optic or electric pumping
• Increased population inversion

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Stimulated Emission

• Incoming photon whose frequency corresponds
• Emitted photon --

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Laser

• Optical Pumping
• Multiple Reflections
• Coherent Light

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Interference in CDs

• Laser shines light onto track of CD
• Discs have pits in the surface
• Sensor reads signal from laser
• CD Burners

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Constructive Interference

• When entire beam reflects from the pit or when
  entire beam reflects from the land
  constructive interference results on

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Destructive Interference

• Pits are ¼ ? above the land
• When part of beam reflects from pit and part
  from land
• Destructive interference interpreted as off

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Laser Scans Disc

• Intensity of the reflected light varies as the
  disc rotates.
• Intensity is measured and interpreted as a series
  of ones and zeros (digital information).
• Information is then relayed to other systems that
  interpret it.

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Holography
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Viewing a Hologram